240 ◾ Fundamental Food Microbiology
Enzymes in Food Waste Treatment
Food industries generate large volumes of both solid and liquid wastes. Waste disposal methods have
used different physical, chemical, and some biological methods. Biological methods include anaerobic digestion and production of SCPs. 18 Because of an increase in regulatory restrictions in waste
disposal, effective and economical alternative methods are being researched. The possibility of using
enzymes to reduce wastes and convert the wastes to value-added products is being developed. The
availability of specific enzymes at low costs has been a major incentive in their use for waste disposal.
Some of the enzymes used in food waste treatments are polysaccharidases (cellulase, pectinase,
hemicellulase, chitinase, and amylase), lactase, and proteinases. Treatment of fruits with cellulase
and pectinase has increased juice yield and improved separation of solids from the juice. The
solids can be used as animal feed. Chitinases are used to depolymerize the shells of shellfish and
the product used to produce SCPs. Amylases are used to treat starch-containing wastewater to
produce glucose syrup for use in alcohol production by yeasts. Lactose in whey has been treated
with lactase (β-galactosidase) to produce glucose and galactose, which are then used in alcohol
production by yeast or to produce baker’s yeasts. Proteases are used to treat wastewater from fish
and meat-processing operations. Some of these products are used as fish food. In recent years,
food processing wastes are now becoming the source of alternative energy, such as methane gas,
ethanol, hydrogen gas, etc., resulting from microbial growth and fermentation. 19
In the future, development of better and low-cost enzymes through recombinant DNA technology will increase their uses in food waste treatment.
Conclusion
The materials discussed in this chapter briefly summarize some of the cell components, metabolic
end products, and enzymes produced by food-grade and regulatory agency–approved microorganisms that are used in foods as additives to improve the nutritional and acceptance qualities of
foods. Recent advances in genetic engineering and metabolic engineering of these bacteria have
helped develop strains that can produce many unique products. As our knowledge on genome
sequences and function of the genes of these strains increases, many new strains will be developed
to produce other unique products. The future potential in this area is very high.
QUESTIONS
1. What are the advantages and disadvantages of using microbial proteins as human food?
2. For each of the following, list one example from microbial origin that is used in food:
amino acids, flavor compounds, flavor enhancers, color, polysaccharides (stabilizers), and
nutraceuticals.
3. Briefly indicate how some lactic acid bacteria can be engineered to produce large quantities
of diacetyl and acetaldehyde (see Chapter 12).
4. Name the microorganisms that are used to produce l(+)-lactic acid, acetic acid, and citric acid.
5. List the advantages and disadvantages of using microbial enzymes and microbial cells in
food processing.
6. List five enzymes of microbial origin and discuss their specific uses in the food industry.
7. Discuss the advantages of using immobilized enzymes in the production of food ingredients.
List three methods of immobilization.
Enzymes in Food Waste Treatment
Food industries generate large volumes of both solid and liquid wastes. Waste disposal methods have
used different physical, chemical, and some biological methods. Biological methods include anaerobic digestion and production of SCPs. 18 Because of an increase in regulatory restrictions in waste
disposal, effective and economical alternative methods are being researched. The possibility of using
enzymes to reduce wastes and convert the wastes to value-added products is being developed. The
availability of specific enzymes at low costs has been a major incentive in their use for waste disposal.
Some of the enzymes used in food waste treatments are polysaccharidases (cellulase, pectinase,
hemicellulase, chitinase, and amylase), lactase, and proteinases. Treatment of fruits with cellulase
and pectinase has increased juice yield and improved separation of solids from the juice. The
solids can be used as animal feed. Chitinases are used to depolymerize the shells of shellfish and
the product used to produce SCPs. Amylases are used to treat starch-containing wastewater to
produce glucose syrup for use in alcohol production by yeasts. Lactose in whey has been treated
with lactase (β-galactosidase) to produce glucose and galactose, which are then used in alcohol
production by yeast or to produce baker’s yeasts. Proteases are used to treat wastewater from fish
and meat-processing operations. Some of these products are used as fish food. In recent years,
food processing wastes are now becoming the source of alternative energy, such as methane gas,
ethanol, hydrogen gas, etc., resulting from microbial growth and fermentation. 19
In the future, development of better and low-cost enzymes through recombinant DNA technology will increase their uses in food waste treatment.
Conclusion
The materials discussed in this chapter briefly summarize some of the cell components, metabolic
end products, and enzymes produced by food-grade and regulatory agency–approved microorganisms that are used in foods as additives to improve the nutritional and acceptance qualities of
foods. Recent advances in genetic engineering and metabolic engineering of these bacteria have
helped develop strains that can produce many unique products. As our knowledge on genome
sequences and function of the genes of these strains increases, many new strains will be developed
to produce other unique products. The future potential in this area is very high.
QUESTIONS
1. What are the advantages and disadvantages of using microbial proteins as human food?
2. For each of the following, list one example from microbial origin that is used in food:
amino acids, flavor compounds, flavor enhancers, color, polysaccharides (stabilizers), and
nutraceuticals.
3. Briefly indicate how some lactic acid bacteria can be engineered to produce large quantities
of diacetyl and acetaldehyde (see Chapter 12).
4. Name the microorganisms that are used to produce l(+)-lactic acid, acetic acid, and citric acid.
5. List the advantages and disadvantages of using microbial enzymes and microbial cells in
food processing.
6. List five enzymes of microbial origin and discuss their specific uses in the food industry.
7. Discuss the advantages of using immobilized enzymes in the production of food ingredients.
List three methods of immobilization.